<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0,user-scale=no">
    <title>Document</title>
    <style>
    body{
        color:white;
        background-color:#222;
    }
    .spot{
        position:absolute;
        width:70px;
        height:70px;
        border-radius:35px;
        box-shadow:0px  0px 40px #fff;
        background-color:#fff;
        opacity:.7;
        }
    </style>
</head>
<body>
    随着手指移动的小圆球
    <script>
        let spot=null;
        document.addEventListener("touchstart",(event)=>{
            event.preventDefault();
            if(spot){
                return;
            }
            spot=document.createElement('div');
            spot.classList.add('spot');
            spot.style.top=event.touches[0].pageY-35+"px";
            spot.style.left=event.touches[0].pageX-35+"px";
            document.body.appendChild(spot);
        },false);
        document.addEventListener("touchmove",(event)=>{
            event.preventDefault;
            if(spot){
                spot.style.top=event.touches[0].pageY-35+"px";
                spot.style.left=event.touches[0].pageX-35+"px";                
            }
        },false);
        document.addEventListener("touchend",(event)=>{
            event.preventDefault();
            if(spot){
                document.body.removeChild(spot);
                spot=null;
            }
        },false);
    </script>
</body>
</html>